The sensory receptors that are the focus of this Program Project Grant (i.e., the vertebrate retina and invertebrate photoreceptor, the arterial chemoreceptors of the mammalian carotid body, and the Merkel cell mechanoreceptor apparatus of mammalian skin) are all generally considered to be 'composite' receptors, in which specialized sensory cells are the transducer elements that ultimately drive the sensory nerve fibers. Sensory transduction in these receptor systems can thus be defined as the sum of chemical and ionic events initiated by an adequate stimulus that occur in the sensory cell/afferent fiber complex of the receptor. As such, sensory transduction involves multiple activity sites (membrane receptors, ionic channels, cellular enzymes, etc.) linked to form a cascade of activity by intracellular and intercellular chemical messengers (second messengers, transmitters, ionic species, etc.) which thereby regulate signal transduction in the receptor. The objective of our proposed Program Project Grant is to elucidate the roles played by chemical messengers in transduction, synaptic coupling, and modulation within both simple and complex sensory processing "units." A multidisciplinary and collaborative approach amongst the projects will be utilized to elucidate the actions of these chemical mediators in receptor function. The six projects encompass three fundamental types of sensation, namely vision, arterial chemoreception and somatosensation. Drs. Lasater and Kolb, and Dr. Brown (Projects #1 and #2) will utilize electrophysiological, pharmacological and immunocytochemical techniques to investigate the role of neurotransmitters and intracellular messenger systems in the transduction and modulation of visual signals in the turtle retina and in the barnacle photoreceptor, respectively. In mammalian carotid body chemoreceptors, the involvement of multiple putative transmits as well as intracellular messengers in stimulus transduction, transmitter interactions and sensory cell coupling (Projects #3 and #4), as well as the co-localization and activity profiles of these substances (Project #5) will comprise the electrophysiological, neurochemical and immunocytochemical studies proposed by Drs. Eyzaguirre, Fidone and Stensaas, respectively. Finally, using these same experimental techniques, Drs. Wei and English (Project #6) will study the physiological role played by putative transmitter substances in touch receptors (Merkel cell 'touch domes') of the cat skin.